Bandwidth requirements continue to drive the need for low-power, high speed interconnects. Harnessing the mature CMOS technology for high volume manufacturing, Silicon Photonics is a top candidate for providing a viable solution for high bandwidth, low cost, low power, and high packing density, optical interconnects. The major drawback of silicon, however, is that it is an indirect bandgap material, and thus cannot produce coherent light. Consequently, different integration schemes of III/V materials on silicon are being explored. An integrated CMOS tunable laser is demonstrated as part of a composite-CMOS integration platform that enables high bandwidth optical interconnects. The integration platform embeds III-V into silicon chips using a metal bonding technique that provides low thermal resistance and avoids lattice mismatch problems. The performance of the laser including side mode suppression ratio, relative intensity noise, and linewidth is summarized.
We describe experimental and theoretical analysis of coupling of light scattered by metal or dielectric nanoparticles into
waveguide modes of InP/InGaAsP quantum-well solar cells. The integration of metal or dielectric nanoparticles above
the quantum-well solar cell device is shown to couple normally incident light into lateral optical propagation paths, with
optical confinement provided by the refractive index contrast between the quantum-well layers and surrounding material.
Photocurrent response spectra yield clear evidence of scattering of photons into the multiple-quantum-well waveguide
structure, and consequently increased photocurrent generation, at wavelengths between the band gaps of the barrier and
quantum-well layers. With minimal optimization, a short-circuit current density increase of 12.9% and 7.3% and power
conversion efficiency increases of 17% and 1% are observed for silica and Au nanoparticles, respectively. A theoretical
approach for calculating the optical coupling is described, and the resulting analysis suggests that extremely high
coupling efficiency can be attained in appropriately designed structures.
An electroabsorption modulator (EAM) is designed to optimize dynamic range performance over 20
GHz bandwidth. The single stripe waveguide enables an extremely compact and integrated package to
be fabricated with single mode fiber pigtails. The transfer function's shape permits suppression of
higher order intermodulation products, yielding a spur-free dynamic range exceeding that of Mach-
Zehnder designs. A dilute optical core diverts energy flow from absorbing layers into low loss
waveguide; the 20 dBm optical power tolerance is significantly higher than that of commercially
available electroabsorption devices. The tunable performance over 20 GHz is characterized and
applications are discussed. New approaches to the broadband impedance matching requirements are
calculated and the impact on system performance is assessed.
Externally coupled electroabsorption modulators (EAM) are commonly used in order to transmit RF signals on
optical fibers. Recently an alternative device design with diluted waveguide structures has been developed. [1] Bench
tests show benefits of lower propagation loss, higher power handling (100 mW), and higher normalized slope efficiency.
This paper addresses the specific issues involved in packaging the diluted waveguide EAM devices. An evaluation
of the device requirements was done relative to the standard processes. Bench tests were performed in order to
characterize the optical coupling of the EAM. The photo current maximum was offset from the optical power output
maximum. The transmissions vs. bias voltage curves were measured, and an XY scanner was used to record the mode
field of the light exiting from the EAM waveguide in each position. The Beam Propagation Method was used to simulate
the mode field and the coupling efficiency. Based on the bench tests and simulation results, a design including
mechanical, optical and RF elements was developed. A Newport Laser Welding system was utilized for fiber placement
and fixation. The laser welding techniques were customized in order to meet the needs of the EAM package design.
We demonstrate the use of an area selective zinc in-diffusion technique as a simple and efficient technique for the
fabrication of integrated photonic devices. In this work, the zinc in-diffusion process has a two fold application. It is well
known that the diffusion of zinc in InP follows an interstitial-substitutional diffusion mechanism. This provides a
concentration dependent diffusion profile, which allows us to control the sharpness of the diffusion front by controlling
the background doping concentration of the semiconductor wafer. By controlling the zinc depth combined with a sharp
diffusion front, the insertion losses of the devices can be minimized. In addition, this results in selective definition of p-n
junctions across the semiconductor wafer and therefore offers the potential for integration with electronic devices. Using
this technique an integrated 2x2 Mach-Zehnder modulator/switch was fabricated. The semiconductor wafer is based on
InGaAsP multiple quantum wells. To selectively define p-n regions for the contacts, we use a 200-nm thick silicon
nitride mask during the diffusion. The Mach-Zehnder structure is then patterned using photolithography and dry etching.
After a cyclotene planarization process, p-type contacts are deposited on top of the diffused regions by evaporation and
lift-off. Our experimental results demonstrate that on-chip losses on the order of 4-dB are obtained, which is
significantly lower compared to the use of isolation trenches. The device response as a modulator requires an additional
insertion loss of 3-dB for voltage controlled operation, with an extinction ratio better than 16 dB. In the case of electrical
current operation, better than 20 dB extinction ratio was obtained with only 8 mA.
We describe novel methods for waveform synthesis and detection relying on longitudinal spectral decomposition of subpicosecond optical pulses. Optical processing is performed in both all-fiber and mixed fiber/free-space systems. Demonstrated applications include ultrafast optical waveform synthesis, microwave spectrum analysis, and high-speed electrical arbitrary waveform generation. The techniques have the potential for time bandwidth products ≥104 due to exclusive reliance on time-domain processing. We introduce the principles of operation and subsequently support these with results from our experimental systems. Both theory and experiments suggest third order dispersion as the principle limitation to large time-bandwidth products. Chirped fiber Bragg gratings offer a route to increasing the number of resolvable spots for use in high speed signal processing applications.
Design for high efficiency, high power traveling wave electroabsorption modulator using Intra-Step-Barrier Quantum Well (IQW) and Peripheral Coupled waveguide (PCW) designs are presented. Both of these designs have separately yielded EAMs with high optical power handling and low Vp properties, in an analog fiber link configuration. The IQW EAM has low Vp (~0.73 V) and high power handling (100 mW). The lumped element IQW EAM has achieved a link gain of -16 dB, a multi-octave SFDR of 110 dB-Hz2/3 and a single-octave SFDR of 121dB-Hz4/5 at the 1543 nm wavelength. The PCW MQW EAM with lumped element configuration can achieve a low link low, a high multi-octave SFDR at the same wavelength. The traveling wave properties of these EAMs are under investigation.
A Radio-over-Fiber system with simplified Base Station (BS) is proposed in which a single chip DBR Reflective Electro-absorption Modulator (REAM) serves both as an optical transceiver and as a mixer at the BS. It enables full duplex optical transmission for base band and RF band services simultaneously due to good isolation between uplink and downlink at the same chip. Grating structure is incorporated into the EA modulator for the sake of system design. It also improves yield and efficiency of high-speed devices.
Electroabsorption modulators (EAM) have been widely used in externally modulated RF link. In the conventional intensity modulation format, the RF efficiency of such link is critically dependent on the optical saturation of the EAM and the fiber dispersion. In an effort to minimize the dependence on these two factors, we have conducted an experimental study of an optical mixer that employs two heterodyned lasers to generate an optical local oscillator (LO). In contrast to the conventional schemes where both laser beams are launched into the same EAM, the EAM in the present scheme modulates only one of the laser beams. In this way, improvement in RF gain is obtained since it is not limited by the optical saturation of the EAM. The resulting optical spectrum shows that this scheme is equivalent to the optical single side band transmission. For sub-octave bandwidth applications, the dispersion effect in the fiber can be ignored.
We report here on wafer-bonded InGaAs/Si avalanche photodiodes (APDs) demonstrating very low excess noise factors that were fabricated using a high-yield, wafer-scale bonding process. The bonding interface quality was evaluated using high-resolution x-ray diffraction and dark current measurements. Measured dark currents on 20 μm diameter mesas are 25 nA and 170 nA at gains of 10 and 50, respectively. Low excess noise factors, which are predicted due to the superior noise properties of Si as a multiplication layer, were measured to be more than 3 times lower than commercial InGaAs/InP APDs at a gain of 10, and more than 9 times lower at a gain of 50. The corresponding electron/hole ionization coefficient ratio k in these devices is as low as 0.02.
This paper proposes the integration of an antenna with a photodetector for high capacity wireless communications. The side-illuminated waveguide photodetector (WGPD) is used to convert the RF-modulated optical power into a microwave signal, which in turn is fed to an antenna. The WGPD is a standard p-i-n device grown on a semi-insulating InP substrate and fabricated using conventional techniques. The performance of this RF/photonic antenna in the frequency range 17-20 GHz is studied theoretically and experimentally. An equivalent circuit model for the WGPD is developed to estimate the photodetector impedance as a function of frequency to assist in the impedance matching between the photodetector and the antenna. The agreement between measurement and circuit model results for the WGPD impedance is very good. It is envisioned that a large number of such RF/Photonic antenna elements could be networked together into a star configuration, feeding in and out of a radio hub.
Wafer-bonded avalanche photodiodes (APDs) combining InGaAs for the absorption layer and silicon for the multiplication layer have been fabricated. The reported APDs have a very low room-temperature dark current density of only 0.7 mA/cm2 at a gain of 10. The dark current level is as low as that of conventional InGaAs/InP APDs. High avalanche gains in excess of 100 are presented. The photodiode responsivity at a wavelength of 1.31 micrometers is 0.64 A/W, achieved without the use of an anti-reflection coating. The RC-limited bandwidth is 1.45 GHz and the gain-bandwidth product is 290 GHz. The excess noise factor F is much lower than that of conventional InP-based APDs, with values of 2.2 at a gain of 10 and 2.3 at a gain of 20. This corresponds to an effective ionization rate ratio keff as low as 0.02. The expected receiver sensitivity for 2.5 Gb/s operation at (lambda) = 1.31 um using our InGaAs/silicon APD is -41 dBm at an optimal gain of M = 80.
We review the electroabsorption (EA) device as a linear mixer for frequency conversion. We explain the operating principle and compare the operation of the EA device as a modulator/mixer with the operation as a detector/mixer. We present experimental results of EA devices with the quantum- confined Stark effect and the Franz-Keldysh effect. Using a InAsP/GaInP multiple-quantum-well EA device, a conversion loss of 18.4 dB is obtained at 10-mW optical local oscillator power when the device is operated as a detector/mixer. The two-tone measurement on the same device shows a sub-octave, spur-free dynamic range of 120.0 dB-Hz. Phase noise measurement demonstrates that very low phase noise is added in the conversion process. We propose a novel full-duplex operation of the EA device as a detector/mixer for the application in the antenna remoting or fiber-radio systems.
Employing photoelastic effect with thermally stable and controllable metal stressor stripes for low propagation loss (on the order of 1 dB/cm) optical waveguide has been achieved in both InP and GaAs based planar waveguides. The study of stressors is based on Ni and WNi stripes. Planar processes, involving both photoelastic WNi stressor and He- implantation, have been used in the fabrication of single- quantum-well photoelastic GaAs/AlGaAs lasers and of the InGaAsP/InP Franz-Keldysh effect electroabsorption waveguide modulators. Get high performance photoelastic semiconductor laser and electroabsorption modulator.
The best RF link gain and the multi-octave SFDR are obtained when the semiconductor EA modulator is biased at the point where the photocurrent has maximum slope efficiency. Since the maximum slope efficiency corresponds directly to the maximum slope of the photocurrent, the photocurrent output is monitored as the applied bias voltage is swept1. The voltage at which the modulator photocurrent changes fastest (highest slope) corresponds to the optimum bias point for maximum link gain. During the sweep, the photocurrent output from the modulator is amplified and sent to a microcontroller. The microcontroller records the photocurrent during the sweep and determines the optimum bias. This is preferable to the common way of determining maximum RF gain by tapping off a portion of the optical power because it does not induce optical loss or require additional optical components. This paper will present the design and testing of a module that will stand alone and apply the optimum dc bias for a modulator automatically.
A new approach for linearizing electroabsorption modulators (EAM) is presented here. It will be very useful for broadband, analog, radio frequency fiber-optic links. In this approach, two or more EAM will be fabricated in series on the same waveguide. Theoretical analysis shows that cancellation of both the second order and third order harmonic distortions can be obtained simultaneously by using proper electrode length and by biasing appropriately the electrodes, leading to an enhancement of the multi-octave spurious free dynamic range (SFDR). Simulation shows that the SFDR of the optical link for the two-electrode case is 10 dB larger than that for a single electrode case. Experimental confirmation of the theoretical prediction on distortion reduction is also presented.
Analog-to-digital converters operating at unprecedented speeds and resolutions are presently under development using a combination of photonics and electronics techniques. These systems impose stringent performance constraints on the photoreceivers used for photonic - electronic conversion, particularly in regard to linearity and noise. Photodetectors must accommodate optical pulses with very high input powers iwthout saturation, and the pulse input energy must be accurately determined. This paper presents design considerations and simulations of photodetectors and associated preamplifiers to meet these goals.
Semiconductor electroabsorption modulator (EAM) is a promising alternative to lithium niobate modulator for digital and analog fiber optic links due to its inherent small size, high modulation efficiency, and potential of monolithic integration with other electronic and optoelectronic components. For high-speed application, the bandwidth of the lumped element EAM is known to be RC-time limited. To achieve an ultra large bandwidth in lumped element EAM, the modulation efficiency has to be greatly sacrificed. This is especially critical in analog operation where RF link loss and noise figure must be minimized. To overcome the RC bandwidth limit and to avoid significantly compromising the modulation efficiency, the traveling wave electroabsorption modulator has been proposed and experimentally investigated by several authors.
High performance photodiodes are essential for photonic insertion into Phased Array Antenna Systems. This paper discusses the RF linearity performance of photodiodes with consideration of thermal effect at high photocurrent, and presents new understandings of both surface-normal and waveguide photodiodes using an equivalent circuit model analysis. The analysis is accompanied by a novel diagnostic technique for robust examination of photodiodes.
Waveguide npin heterojunction phototransistors (HPTs) are investigated for analog fiber-optic link applications. The device is fabricated on a semi-insulating InP substrate with an integrated CPW transmission line. At low optical power, an incremental DC responsivity of approximately 16 A/W is observed at 1.3 micrometers wavelength. It is demonstrated that the HPT responsivity at RF frequencies can be increased through a second optical beam. Signal mixing experiment using two RF-modulated optical beams shows that the waveguide npin HPT can be used as an effective integrated photodetector/mixer for RF signal up- and down-conversion.
A novel npin waveguide structure for the dual-function electroabsorption modulator/detector is proposed and fabricated. With the addition of an n-layer to the conventional pin-structure, the device exhibits phototransistor behavior in the detector model. The device has an InGaAsP intrinsic layer with Franz-Keldysh electroabsorption at 1.3 micrometers wavelength. Preliminary results show optical gain in the detector mode and good modulator characteristics.
Analog fiber optic links can be used to transmit microwave and millimeter wave signals in applications such as cable TV, antenna remoting and active phased array. In this paper, we examine various issues pertaining to an integrated laser- modulator transmitter module for analog fiber optic links: (1) the performance requirements of the lasers, (2) the performance requirements of the electroabsorption modulator, (3) the bias control of the electroabsorption modulator.
External modulation of cw laser radiation by multiple quantum well electroabsorption modulators will potentially play an important role in rf photonic links, especially at high microwave frequencies and millimeter waves. InAsP/GaInP MQW on InP and GaInAs/InAlAs MQW on GaAs modulators have been grown by MBE and fabricated into p-i-n modulators. Performance with -26 dB link efficiency without amplification, 5 dB insertion loss, 15 mW of optical power and 17 GHz bandwidth has been experimentally demonstrated. Extension to 100 GHz bandwidth with -39 dB link efficiency (without amplification) can be expected. Traveling wave modulators and on-chip impedance matching of p-i-n modulators have been designed, fabricated and evaluated. Traveling wave modulators with flat frequency response over 40 GHz have been experimentally demonstrated.
Planar photoelastic effect on compound semiconductor structures has been investigated for integrated optical transmitter in rf photonics system. While our prior works emphasized the investigation of low-loss photoelastic waveguide, photoelastic waveguide modulator, and photoelastic optical splitter, the present work focuses on the attainment of high performance laser which employs the photoelastic effect for waveguiding. Planar separate- confinement, double-heterostructure, single-quantum-well photoelastic GaAs/AlGaAs lasers have been fabricated using WNi stressors for waveguiding and ion implantation for isolation. Even without bonded on heat-sinks, these planar photoelastic lasers operate continuous wave at room temperature. The lowest threshold is 29 mA for a cavity length of 178 micrometers and a stressor width of 5 micrometers . The main waveguiding mechanism of the photoelastic lasers is determined to be weak index-guiding with the beam waist in the junction plane measured at 10 micrometers behind the end- facet.
A Franz-Keldysh effect InGaAsP electroabsorption waveguide device is utilized as the high-frequency, high-linear dynamic range modulator and photodetector. The dual-function modulator/photodetector can be useful in compact transmit/receive front end antenna architectures. Adjusting the electrical bias to the reverse-biased p-i-n diode, either efficient optical modulation or detection is demonstrated. As an electroabsorption modulator, a fiber optic link with a minus 17.4 dB rf loss and a 124 dB-Hz4/5 sub-octave spurious-free dynamic range is obtained with electrical biases in the 2 to 3 V range. As a waveguide photodetector, a 0.47 A/W fiber coupled responsivity, photocurrents up to 20 mA, and an output second-order intercept of plus 34.5 dBm are achieved at 7 V electrical bias. Supporting measurements on additional test devices show a trend toward larger intercept point with longer device lengths.
KEYWORDS: Modulators, Waveguides, Planar waveguides, Photoelasticity, Ion implantation, Capacitance, Helium, Near field optics, Signal attenuation, Thin film devices
Planar electroabsorption InP/InGaAsP waveguide modulators suitable for RF applications have been fabricated using the photoelastic effect. The planar device structure is achieved by using WNi thin film surface stressors for lateral waveguiding and helium implantation for electrical isolation between devices. These are the first reported frequency measurements on a photoelastic InP/InGaAsP waveguide modulator.
A four-layer asymmetric waveguide structure using a nonabsorbing 1.08 eV bandgap InGaAsP waveguiding layer has been studied for high saturation power, high speed waveguide photodiode operating at 1.32 micrometers wavelength. A peak photocurrent of 32 mA corresponding to an optical power of 76 mW has been obtained for 40 GHz waveguide photodiode.
To implement millimeter wave photonic links using high speed optical modulators, RF input efficiency to the modulator is an important consideration. In this paper we discuss design and fabrication of ultra high speed multiple quantum well electro-absorption modulators for narrow band applications up to 40 GHz. In order to obtain higher RF efficiency at working frequencies of 20 GHz, 25 GHz and 40 GHz, modulators with monolithically integrated matching circuits were designed and fabricated utilizing co-planar waveguide MMIC technologies. Measurement results show excellent matching at specific frequencies with S11 of -16 dB for the 20 GHz devices, -20 dB for the 25 GHz devices and -36 dB for the 40 GHz devices. At least 6 dB of improvement on optical modulation efficiency can be expected over modulators without impedance matching.
Large spurious-free dynamic range (SFDR) has been measured in a fiber optic link using an InGaAsP electroabsorption (EA) waveguide modulator. Link phase noise is investigated and conversion of AM noise to phase noise appears to be an issue in the EA device. Preliminary measurements of the EA link show inferior close-to-carrier phase noise compared to a link using a Mach-Zehnder modulator with similar SFDR. Optical feedback from the output coupling fiber is shown to contribute partially to close-in phase noise.
Optically transparent time-division multiplexors and switches can be used to create terabit packet-switched networks. Cascaded optical delay (COD) multiplexors are modular, buffered 2:1 statistical packet multiplexors build from 'smart' crossbars and fiber delay lines. We have implemented the fundamental unit of COD multiplexors, a memoryless 2:1 packet multiplexor. It accepts fixed-length packets. It is designed to handle slotted and unslotted traffic, so it does not require network synchronization. This multiplexor has been built using off-the-shelf components. We demonstrate its switching characteristics for 340 ns packets, as well as present its measured packet loss rate. It can be used to make larger, buffered multiplexors with improved packet loss rates. We present the statistical insertion los distribution associated with buffered COD multiplexors. Furthermore, we outline a method of optical loss compensation which eliminates the insertion loss distribution.
We have constructed an optical 2-to-1 packet multiplexor for use in the next generation of digital networks. It has a clear advantage over conventional electronic network nodes because it can support any bit rate, theoretically up to the full bandwidth of a fiber. Since it switches on a packet-by-packet basis, the control electronics are simple and inexpensive. The multiplexor uses electronically-addressed 2 X 2 lithium niobate directional coupler switches to route packets and lengths of fiber to buffer contentious packets. The multiplexor can be cascaded to form a larger 2-to-1 multiplexor with improved packet loss performance. We present theoretical and simulated results (including packet loss rate and optical insertion loss) for this multiplexor. We also contrast the performance of the multiplexor for slotted input versus unslotted input.
KEYWORDS: Visualization, Diagnostics, Switching, Radiology, Switches, Data archive systems, Radio optics, Sensors, Medical imaging, Magnetic resonance imaging
The next generation of distributed imaging and visualization environments for diagnostic radiography and C4I will require the delivery of a guaranteed quality-of-service by a ultra-high bit rate network. Two aspects of the quality-of-service, the link bit rate and the round-trip packet latency, can be met through the use of transparent third-generation photonic networks. These networks can be implemented using ultra-short optical pulses in conjunction with spectral-domain processing to construct links. These links are combined with transparent photonic packet switches to form the network switching fabric. The quality-of-service is guaranteed by using virtual circuit-switching.
Comparable gain can be obtained in semiconductor optical amplifiers (SOAs) with either bulk or strained-layer multiple quantum well (MQW) active layer. Their polarization dependence and saturation power are affected by strain and structure designs. In this study, SOAs with compressively strained MQWs have exhibited highest gain and saturation power, while buried waveguide SOAs with large optical cavity have lower polarization sensitivity than the ridge waveguide SOAs.
Chaotic stability of external cavity semiconductor laser under modulation is examined both theoretically and experimentally. When the modulation frequency is detuned below the cavity resonant frequency, the simulations show a two-frequency to three-frequency route to chaos, as depicted by the power spectrum and time series of the laser emission at different stages of detuning. This agrees with experimental observations of 1.3 micrometer wavelength distributed feedback (DFB) laser and ridge waveguide (RW) InGaAsP laser. The phase-space attractor of both DFB and RW lasers have well-defined structures at broadband chaotic state, which signifies the presence of dynamical determinism in this state.
KEYWORDS: Modulators, Intermodulation, Waveguides, Sensors, Distortion, Signal detection, High dynamic range imaging, Analog electronics, Modulation, Polarization
The Franz-Keldysh effect is utilized for high-linearity, electroabsorptive InGaAsP waveguide modulators. Two-tome RF measurements are performed in which the DC bias is adjusted to maximize the spurious-free linear dynamic range. With the proper choice of bias, the sub- octave link dynamic range increases to 123 dB in a 1 Hz bandwidth for 0.25 mA photocurrent.
A fully packaged and connectorized 1.32 micrometers InGaAsP electroabsorption modulator for analog fiber optic link applications is described. This Franz-Keldysh effect modulator has a 3-dBe bandwidth exceeding 20 GHz, a fiber-to-fiber optical insertion loss of less than 9 dB, and a high modulation efficiency (equivalent switching voltage less than 10 V). A fiber link spurious free dynamic range of greater than 100 dB in a 1 Hz bandwidth is achievable using this modulator, which makes it attractive for Navy shipboard applications.
High-frequency and high-responsivity photodetectors which possess a high saturation intensity are needed for high performance analog fiber optic links. We report the results of a high saturation intensity InGaAs/InP PIN waveguide photodetector. At an optical wavelength of 1.3 micrometers , the detector has a responsivity of 0.5 A/W and a flat frequency response from 800 MHz to 20 GHz. With a bias of -4 V, the normalized frequency response of the detector remains unchanged when optical powers up to 10 mW are incident on the detector. An initial linearity measurement is made by measuring the linearity of a fiber optic link which uses the detector with a DC photocurrent of 140 (mu) A as the receiver. The linearity of the link is limited by the modulator of the link and there is no detectable nonlinearity introduced by the detector.
To implement high-bandwidth optical analog or digital communication links based on optical modulators, ultrahigh performance modulator driver amplifiers are required. Design considerations for such amplifiers are discussed here. Designs are significantly different than for laser driver amplifiers. For modulator drivers, an emitter follower output stage is appropriate. Active pull-down circuitry is beneficial to reduce power dissipation in a digital driver. Inductive tuning is beneficial to extend frequency response. Flip-chip mounting is beneficial to reduce bonding parasitic capacitance. Examples are given for driver designs for 10Gbit/s digital applications, and for 20GHz analog links, employing GaAs/AlGaAs HBT technology.
Strained balanced InAsP/InGaP superlattices for optoelectronic applications were studied with materials grown by low pressure MOVPE. For 20 and 30 period InAsP/InGaP superlattices with a 23 percent As mole fraction in the InAsP layers, sharp x-ray satellite peaks are obtained. The superlattices show an average lattice constant close to that of the InP substrate. Strong photoluminescence with narrow emission linewidth are observed at room temperature around 1.11 micrometers . PIN diodes with an intrinsic region consisting of the InAsP/InGaP superlattice show efficient electroabsorption at wavelengths around 1.15 micrometers with a small residual absorption of 59 cm-1.
We report results of an improved hybrid optical transmitter suitable for use in microwave communication systems. Based on a double up-conversion technique, a 1.3 micrometers wavelength semiconductor diode laser is actively mode-locked, and its output is externally modulated by a lithium niobate Mach-Zehnder amplitude modulator to generate a transmitter output from 19 GHz to 21 GHz. Following a brief review of recent table top system measurements and motivation, we show a second generation engineering scheme for packaging the mode-locked source components. The initial performance results of this source are -34.2 dBm(e) mode-locked output power at 13.1 GHz, with an input rf power of 14.5 dBm(e); RIN is measured at -106.5 dBc(e)/Hz.
InGaAs/InP multiple quantum well electroabsorption modulators grown by MOCVD are designed and fabricated for 1.5 micrometers wavelength operation. For rib loaded waveguide modulators fabricated on n-InP substrate with a 3 micrometers rib width and a 2 micrometers intrinsic waveguide layer, a capacitance of 0.2 to 0.3 pF and a reverse breakdown voltage > 20 V are obtained. The extinction ratio of the modulators is more than 14 dB and the 3 dB optical bandwidth is 18 GHz. The modulator's RF efficiency and optical insertion loss still need to be improved. For modulators made on semi-insulating InP substrate, a capacitance in the range 0.1 to 0.2 pF is measured.
A 1.3-micron wavelength optical transmitter system with a 2-GHz bandwidth centered at 20 GHz has been implemented by actively mode-locking a semiconductor laser diode and then modulating the signal externally. The performance of a link using this transmitter over a 2-km fiber is evaluated. A hybrid package is developed for a mode-locked laser submodule operating at 15 GHz.
We demonstrate a 1.3 micron wavelength optical transmitter system with a 20 GHz RF center frequency and 2 GHz bandwidth. We accomplish this by actively modelocking a semiconductor diode laser at 14 GHz; the modelocked signal is then externally modulated between 5 GHz and 7 GHz, using a lithium niobate based Mach-Zehnder modulator. We show a hybrid prototype package for the modelocked laser source.
The use of III-V semiconductor heterojunction and quantum well optical modulators is considered for monitoring of shipboard radar and communication emissions. Both antenna- coupled and all-dielectric electro-optic electromagnetic environment monitoring systems are investigated with respect to sensitivity, linear dynamic range, and system bandwidth at optical wavelengths of 1.3 and 1.5 micrometers . Results are presented which indicate that these devices can, if carefully designed and utilized, be a useful alternative to interferometric modulators for this ultra-wideband analog fiberoptic application.
A novel bridge type optoelectric (OE) sample and hold circuit based upon current steering is proposed for the first time and is experimentally tested. Experimental comparison between this circuit and the conventional direct OE sample and hold circuit shows that the bridge type is clearly superior in performance to the direct OE circuit. When a high speed signal is sampled with high accuracy, the bridge type OE sample and hold circuit offers high charging capability, commanding signal isolation, and reduced time jitter, distinct advantages over electronic sample and hold circuits.
The effects of fabrication tolerances on the resonant frequency of Bragg gratings etched in glass waveguides are reported. The glass materials are chosen for low thermal drift of refractive index and consequent low thermal drift of Bragg resonant frequency. Fabrication and measurement of Bragg gratings with grating period held constant to 100 ppm are demonstrated. A monolithic array of notch filters with resonant frequencies shifted over a 5 nm range by choice of waveguide width, thickness, etc., is demonstrated.
The measurement of the relative intensity noise (RIN) of a ridge waveguide laser and a distributed feedback laser under CW, external cavity, direct modulation, and modelocking conditions is presented. The purpose is to determine the relative noise performance of modelocked laser diodes. The results indicate that the RIN of modelocked lasers are comparable to CW lasers but lower than both external cavity lasers (optimized for modelocking but without the applied RF) and directly modulated lasers; the difference can be as much as 5 optical dB. The microwave carriers produced optically by the direct modulation and modelocking of laser diodes are also compared. The comparison determines that modelocked lasers produce less noisy and more RF power efficient microwave carriers. However, no difference in microwave linewidth is detected within the limit of the resolution bandwidth of the detection system.
The performance of the high speed InGaAsP ridge waveguide lasers and the GaAlAs single-mode lasers operating as a micromixer have been investigated by using a circuit model derived from the iterative method and device rate equations. The laser mixer has many advantages over the conventional microwave mixer, including: high conversion gain, wide dynamic range, low noise figure and high local oscillator/intermediate frequency (LO/IF) isolation. The analytic results also indicate that the heterodyne microwave fiber optic link using a laser mixer provides the advantages of system simplicity, cost-effectiveness and improved system signal-to-noise ratio (SNR) than the conventional microwave fiber optic links. System SNR of two fiber optic links were measured: a 12 GHz link with 70 MHz IF has a SNR of better than 120 dB/Hz and a 26.5 GHz up-converted link has a SNR of 100 dB/Hz, without laser diode RF impedance matching. Other system applications of the laser mixer are also presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.